Telephone system.



No. 845,056. PATENTED FEB. 26, 1907.

' E. R. CORWIN. v

TELEPHONE SYSTEM.

APFLIUAIION TILED 0OT.20, 1906. m

FIGJS WITNESSES: INVENTOR E.R. coRWIN ATTORNEY By W.

rm: NoRRls PETERS ca, WASHINGTON, n. c.

UNITE STATES ra'rnn'r enrich.

Specification of Letters Patent.

Patented Feb. 26, 1907.

Application filed October 20,1906- Serial No. 339.851-

T0 at whmn it nuw concern.-

Be it known that I, ELMER R. CoRwIN, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented a certain new and useful Improvement in Telephone Systems, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to common-battery telephone systems, and has for its particular object such an improvement of these systems that will enable a decided simplification of substation apparatus and improvement in its operation.

My invention relates particularly to that v class of common-battery telephone systems in which the transmitters at the substations are included directly in telephone-lines and at which substations impedance-coils are employed, through which the battery-current is fed to the transmitters, these impedancecoils forcing the telephone-currents that come into the substations to pass through the receivers thereat. In systems of this character it has been customary normally to disconnect the receivers as well as the transmitters from the telephone-lines through the agency of switch-hooks sufliciently to open the circuits of these devices, and in order to prevent clicks in the ears of the subscribers, such as might occur when the switch-hooks are vibrated, it has been proposed to provide shortcircuits for the receivers which would be momentarily established as the switchhooks would rise, these short circuits being established about the receivers until the transmitter-circuits have been closed, whereafter in the further operation of the switchhooks the short circuits about the receivers will. be opened, whereupon telephonic connection between the substations and their lines will be completely established.

By means of one feature of my invention I eliminate the short circuits and prevent objectionable clicks in the receivers, as I so arrange the receiver-contacts and the transmitter-contacts as to cause the transmittercircuits to be closed before the receiver-circuits. This result is enhanced by employing in connection with this feature of my invention another feature of my invention, which latter feature resides in making the resistance of the IGCGIVGIECIIGUIC high as compared with the resistance of the impedance-coil.

By this feature of the invention the flow of current through the receiver is materially decreased. This latter feature of my invention is also of service irrespective of the order in I which the receiver and transmitter-circuits are closed. This feature of my invention endispense with the condensers i that have been included in the receiver-cir- I cults for the purpose of preventing the flow of battery-current through the receiver-cir cuits, and thereby prevent the polarization of the receivers. l have demonstrated by actual commercial operation that the use of the condensers is not required when this feature of my invention is practiced at substations, having had telephone systems in actual commercial operation embodying this feature of my invention for a year and a half at Port Angelus, Washington, and at Chicago, Illi- I10lS.

Good results are also obtained when a transmitter of very low resistance is selected to be included in the same circuit connection with the impedance-coil, which circuit connection is shunted by the receiver that is,

where a conductor common to the receiver and transmitter-circuits is employed the condenser may be omitted, even though the transmitter and impedance-coil be included in said common portion, providing the aggregate resistance of said common portion is very low as compared with the resistance of the receiver.

I will explain my invention more fully by reference to the accompanying drawings, in which- Figure 1 diagrammatically illustrates a telephone system equipped in accordance with the invention. Fig. 2 illustrates a mechanical construction in practicing the preferred embodiment of the invention. Fig. 3 indicates a modification of the substation-circuits shown in Fig. 1.

Like parts are indicated by similar characters of reference throughout the different figures.

There are indicated two substations A B,

' each having a transmitter 1, a receiver 2, a call-bell 3, a switch-hook 4., a condenser 5,

that may be employed the telephone-receivers are removed from their hooks the bridges, including said signaling-bells, are opened, the transmitters are I thrown into conductive connection with the lines, whereby battery may be fed thereto through the impedance-coil 6 and whereby voice-currents may be impressed upon the l lines at the substations at the transmitters or may be received at the receivers which are in shunt relation to the impedance-coils, the terminals of the impedance-coils and the terminals of the receivers being directly connected to the exclusion of other substation apparatus, according to the system of Fig. 2, such direct connection of the receiver with the terminals of the impedance-coil being metallic, particularly where the second feature of my invention is practiced.

Each telephone-station is connected by the limbs 7 8 of its telephone-line with the jack-contacts 9 10 at the exchange, at which exchange I have indicated a link conductor, in this instance comprising plugs 11 12 united by tip and sleeve strands, each including a condenser 13, in bridge of which strands a common battery 14 is placed, which common battery is fed through impedance de vices 15 15 to the cord-strands at points be tween which the condensers 13 are located, current fromthis common battery finding its passage through the impedance-coils 6 and transmitters 1 when lines are in telephonic connection.

In avoiding objectionable clicks in the receivers I so mechanically dispose the switch hooks 4 with reference to the contact-terminals 16 17, belonging to the impedancecoils and receivers, that the contact-terminals 16 are brought into connection with the switch-hooks 4 before the contacts 17 are brought into connection with said switchhooks, whereby the circuit ofthe battery 14 is established through the impedancercils before it is established through the receivers. To this end I prefer the mechanical construction illustrated in Fig. 2, which construction will be readily understood, as the parts therein similar to the parts shown in Fig. 1 are iven similar characters of reference. make the impedance-coils 6 of very low ohmic resistance, a resistance of five ohms being preferred. 1 make the resistance of the receivers high, a resistance of one hundred and fifty ohms being preferred therefor, the resistance of the receivers being therefore preferably thirty times the resistance of the impedance-coils. 1

Hitherto circuits such as are exhibited in United States Patent No. 747,339, issued December 15, 1903, to W. V. Dean, have 1 been employed, in which systems the receivers have been of ninety ohms resistance and the impedance-coils of twenty-five ohms resistance, the receivers being less than four times the resistance of the impedance-coils. l

It is because of the fact that the resistance of the impedance-coils have so closely ap proached the resistance of the receivers in such systems as are exhibited in said patent that condensers have had to be included in the local receiver-circuits to prevent the flow of direct current which would polarize the receivers. high resistance as compared with the impedance-coils as hitherto outlined I am enabled metallically to connect the receivers in shunt of the impedance-coils, whereby said. receivers may properly receive incoming voice-currents, and although they at the same time may receive battery-current such current flows through the receivers in such small quantity as to prevent the receivers from being polarized, as I have proven by actual practical test during a year and a half, whereby the employment of condensers provided solely for the special purpose of preventing the receivers from being polarized may be dispensed with, it being obvious that such condensers would have to be employed where the resistances of the receivers and impedance-coils so closely approach as in the systems of the prior art. A While I make and break the shunts, including the receivers, by the switch-hooks, I do not wish to be limited to the.switchhook control of the receiver-circuits.

Another advantage in the apparatus of my present invention over the apparatus of the prior art resides in the fact current passing over the line of a subscriber whose telephone is oil its hook will not find appreciable access to the receiver, which would not be the case if the receiver were of lower resistance and the impedance-coil were of higher resistance, whether or not the receiver-circuit included a condenser.

According to the system shown in Fig. 3, good results are also obtained when a transmitter 1 of very low resistance is selected to be included in the same circuit connection with the impedance-coil 6, which circuit connection is shunted by the receiver that is, where a conductor common to the receiver and transmitter circuits is employed the condenser may be omitted, even though the transmitter and impedance-coil be included in said common portion, providing the aggregate resistance of said common portion is very low as com ared with the resistance of the receiver. 0 practice the invention as indicated in Fig. 3, the impedance-coil is preferably made of four ohms resistance and the transmitter of one ohm resistance quiet. Obviously the switch-hook is usually not vibrated when the transmitter is being spoken into, so that the resistance of the transmitter when in action need not be taken into consideration.

In Fig. 1 the circuits for the receivers and transmitters are closed by the switch-hooks,

Bymaking the receivers of that calling- 1 rent from the common battery, a receiver, a conductively-continuous portion for supplybatterycurrent being common to the receiver and line-circuits and including the impedance-coil, said receiver being in conductively-continuous shunt of said conductivelycontinuous portion, said receiver being of high resistance with respect to the resistance of said conductively-continuous portion, whereby the flow of direct current therethrough is sufficiently eliminated to prevent polarization thereof, and a switch-hook for connecting the transmitter and impedancecoil in the line-circuit and for connecting the receiver in shunt of said conductively-continuous portion, said switch-hook having as contacts a terminal of said conductively-con tinuous portion and a terminal of the receiver, said switch-hook and contacts being so relatively disposed that the switch-hook in being freed of the receiver, will have electrical connection with the first aforesaid contact before it has connection with the receiver-contact, whereby the receiver-circuit will be es tablished after the transmitter-circuit.

common battery subscribers line equipment, including a telephone-line extending to the subscriber's station, a transmitter and impedance-coil adapted for con ductively-continuous inclusion in the line-circuit to receive current from a common battery, a receiver, a conductively-continuous portion common to the receiver and line-circuits and including the impedance-coil, said receiver being adapted for connection in shunt and I claim herein the circuit arrangement irrespective of the manner or the order in which the circuits are realized.

I have indicated a certain type of cord 1 connecting apparatus at the exchange but I do not wish to be limited to any particular i type of cord connecting apparatus. I have I illustrated metallic-circuit telephone-lines; but it is obvious that the invention need not be restricted thereto. I have omitted many details of telephone-exchange systems employed at the exchange, as an illustration t ereof in my present application is not essential to an understanding of my present invention.

Having thus described my invention, I claim as new and desire to secure by Letters Patent 1. A common-battery subscribers-line equipment, including a telephone-line extending to the subscribers station, a transmitter and impedance-coil conductively-included in the line-circuit to receive direct current from the common battery, and a receiver in direct conouctively-continuous shunt of the impedance-coil, said receiver being of high resistance with respect to the resistance the impedance-coil, whereby the flow of direct-current therethrough is sufliciently eliminated to prevent polarization thereof, and the use of a condenser in circuit l with the receiver to prevent its polarization is i not required. I 2. A common-battery subscribersline I equipment, including a telephone-line extending to the subscribers station, a trans mitter and impedance-coil conductively included. in the line-circuit to receive direct cur rent from the common battery, and a receiver, a conductively-continuous portion for sup i plying battery-curent being common to the receiver and line-circuits and including the I of said conductively-continuous portion, and a switclrhook for connecting the transmitter and impedance-coil in the line-circuit and for connecting the receiver in shunt of said conductively-continuous portion, said switchhook having as contacts a terminal of said conductively-continuous portion and a terminal of the receiver, said switch-hook and contacts being so relatively disposed that the switch-hook in being freed of the receiver will have electrical connection with the first aforesaid contact before it has connection with the receiver-contact, whereby circuit through the receiver is established after the transmitter-circuit.

In witness whereof I hereunto subscribe my name this 17th dayof October, A. D. 1906.

ELMER R. OO'RI/VIN.

impedance-coil, said receiver being in con ductively-continuous shunt of said conductively-continuous portion, said receiver being of high resistance with respect to the resistance of said conductively-continuous portion, whereby the flow of direct current theretln'ough is sufficiently eliminated to prevent polarization thereof, and the use of a condenser in circuit with the receiver to prevent its polarization is not required.

3. A common-battery subscribers-line equipment, including a telephone-line extending to the subscribers station, a trans- Witnesses: nutter and impedance-coil conductively inl LEON G. STROH, cluded in the linec1rcu1t to receive direct cur- G. L. CRAGG.

IOC 

